1. Field of the Invention
The present invention relates to a thermoplastic resin composition excellent in rigidity and impact resistance, and provides, when molded, a molded article having a excellent appearance, particularly few flow marks. Further, the present invention relates to an injection-molded article of the thermoplastic resin composition.
2. Description of Related Arts
Polypropylene-based resins have been widely used in materials requiring rigidity, impact strength and the like. Recently, polypropylene-based resins are increasingly used, particularly, as automobile materials, and especially, ethylene-propylene block copolymers are used increasingly. Though ethylene-propylene block copolymers have been conventionally produced by a solvent method, the ethylene-propylene block copolymers are recently produced by a continuous gas phase method which is simple in a production process and can produce the ethylene-propylene block copolymer at low cost.
However, the ethylene-propylene block copolymer produced by the gas phase method has, in general, problems that, due to lower intrinsic viscosity [xcex7]EP of an ethylene-propylene copolymer portion, swelling ratio (SR) is low, flow marks are many and appearance of a molded article deteriorates, further that when the intrinsic viscosity [xcex7]EP of an ethylene-propylene copolymer portion of the ethylene-propylene block copolymer produced by a gas phase method is increased, a granular structure is generated and appearance of a molded article deteriorates.
For solving the problems regarding appearance as described above, for example, JP-A-07-286022 discloses a propylene-based block copolymer produced by a batch-wise solvent method, which has a intrinsic viscosity of an n-decane-insoluble component at 23xc2x0 C. of 0.1 to 20 dl/g, has a intrinsic viscosity of an n-decane-soluble component at 23xc2x0 C. of 5 to 15 dl/g, and can form a molded article without generating a gel on the appearance. However, as disclosed in Comparative Example 3 thereof, an ethylene-propylene block copolymer showing higher intrinsic viscosity of an n-decane-soluble component at 23xc2x0 C. which is supposed to correspond to an ethylene-propylene block copolymer portion contains a lot of rubber granules causing gels.
Further, JP-A-07-286075 discloses a propylene polymer composition which contains a propylene polymer produced according to continuous mode and an ethylene-propylene block copolymer showing a intrinsic viscosity of an n-decane-soluble component at 23xc2x0 C. of 5 to 12 dl/g, and can form a molded article generating no gels on appearance. However, the amount of the ethylene-propylene block copolymer compounded is as high as 12% by weight or more.
An object of the present invention is to provide a thermoplastic resin composition having an excellent stiffness, impact resistance and flowability, and providing, when molded, a molded article having a excellent appearance, particularly few flow marks, and an injection-molded article obtained by using the thermoplastic resin composition.
Under the situations, the present inventors have intensively studied, and resultantly found that the above-mentioned problems can be solved by a thermoplastic resin composition comprising a polypropylene-based resin, elastomer, inorganic filler, and an extremely small amount of a resin having specific melt tension (MT), specific swelling ratio (SR) and specific time required until the ratio of the relaxation modulus G(t) to the relaxation modulus G(0.02) in a time of 0.02 sec. reaches 0.01, and an injection-molded article obtained by using the resin composition, leading to completion of the present invention.
Namely, the present invention relates to a thermoplastic resin composition comprising:
(A) a polypropylene-based resin of 35 to 85% by weight;
(B) an elastomer of 10 to 35% by weight;
(C) an inorganic filler of 2 to 30% by weight; and
(D) a resin of 0.1% by weight or more and less than 5% by weight, wherein (1) the melt tension of the resin (D) measured at a temperature of 190xc2x0 C. and a winding rate of 15.7 m/min. is 0.1 N or more, (2) the swelling ratio of the resin (D) measured at a temperature of 220xc2x0 C., an L/D ratio of an orifice of 40 and a shear rate of 1.2xc3x97103 secxe2x88x921 is 1.8 or more, and (3) the time required until the ratio (G(t)/G(0.02)) of the relaxation elastic modulus G(t) measured at 210xc2x0 C. to there laxation elastic modulus G(0.02) in a time of 0.02 sec. reaches 0.01, of the resin (D) is 10 sec. or more, and wherein the sum of the (A), (B), (C) and (D) is 100% by weight.
Further, the present invention relates to an injection-molded article obtained by using the above-mentioned thermoplastic resin composition.
The present invention will be illustrated in detail below.
The propylene-based resin (A) used in the present invention is not particularly restricted, and preferably, is a crystalline polypropylene-based resin, and examples thereof include a crystalline propylene homopolymer, crystalline ethylene-propylene copolymer, crystalline propylene-xcex1-olefin copolymer and the like, and these may be used alone or in a combination of two or more.
The xcex1-olefin used in the crystalline propylene-xcex1-olefin copolymer is an xcex1-olefin having 4 or more carbon atoms, preferably 4 to 20 carbon atoms, more preferably 4 to 12 carbon atoms, and examples thereof include butene-1, pentene-1, hexene-1, heptene-1, octene-1, decene-1 and the like. Examples of the crystalline propylene-xcex1-olefin copolymer include a crystalline propylene-butene-1 copolymer, crystalline propylene-hexene-1 copolymer and the like.
Further, the crystalline polypropylene-based resin is preferably a crystalline propylene homopolymer, a crystalline ethylene-propylene block copolymer or a mixture of thereof, more preferably a crystalline ethylene-propylene block copolymer or a mixture of a crystalline propylene homopolymer and a crystalline ethylene-propylene block copolymer.
The crystalline ethylene-propylene block copolymer used in the present invention is a crystalline ethylene-propylene block copolymer composed of a propylene homopolymer portion (referred to as xe2x80x9cfirst segmentxe2x80x9d) and an ethylene-propylene random copolymer portion (referred to as xe2x80x9csecond segmentxe2x80x9d).
The propylene homopolymer portion as the first segment has a Q value which is a ratio of weight average molecular weight (Mw)/number average molecular weight (Mn) according to a gel permeation chromatography (GPC) method of preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5. The first segment has preferably an isotactic pentad fraction calculated based on 13C-NMR of preferably 0.98 or more, more preferably 0.99 or more. Further, the intrinsic viscosity [xcex7]P of a tetralin solution at 135xc2x0 C. of the first segment is preferably from 0.7 to 1.1 dl/g, more preferably from 0.8 to 1.0 dl/g.
The ethylene-propylene random copolymer portion as the second segment, has an intrinsic viscosity [xcex7]EP of a tetralin solution at 135xc2x0 C. of from 1.0 or more and less than 8.0 dl/g, preferably from 1.5 to 7.5 dl/g. Further, the second segment has an ethylene content [(C2xe2x80x2)EP] of preferably from 25 to 35% by weight, more preferably from 27 to 33% by weight.
The weight ratio of the ethylene-propylene random copolymer portion (second segment) to the propylene homopolymer portion (first segment) (second segment/first segment ratio) is preferably 8/92 to 35/65.
The crystalline propylene homopolymer used in the above-mentioned mixture with the crystalline ethylene-propylene block copolymer is a polymer having physical properties similar to those of the propylene homopolymer portion which is the first segment of the crystalline ethylene-propylene block copolymer, and specifically having a Q value which is ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) according to a gel permeation chromatography (GPC) method of preferably from 3.0 to 5.0, more preferably from 3.5 to 4.5. This crystalline homopolymer has an isotactic pentad fraction calculated based on 13C-NMR of preferably 0.98 or more, more preferably 0.99 or more. Further, this crystalline homopolymer shows a intrinsic viscosity [xcex7]P of a tetralin solution at 135xc2x0 C. of preferably from 0.7 to 1.1 dl/g, more preferably from 0.8 to 1.0 dl/g.
A method for producing the polypropylene-based resin used in the present invention is not particularly restricted, and the polypropylene-based resin can be produced, for example, by a know n polymerization method such as a bulk polymerization method, solution polymerization method, slurry polymerization method or gas phase polymerization method, or any combination of these polymerization methods, using a known stereoregular olefin polymerization catalyst such as a Ziegler-Natta catalyst system, a metallocene catalyst system or a combination thereof, and a continuous gas phase polymerization method is preferable.
Particularly, the crystalline ethylene-propylene block copolymer is preferably that which is produced by homopolymerizing propylene in the presence of a stereoregular olefin polymerization catalyst in the first step to obtain a crystalline propylene homopolymer portion as a first segment, and subsequently copolymerizing ethylene and propylene in the second step to obtain an ethylene-propylene random copolymer portion as a second segment.
The compounding proportion of the polypropylene-based resin (A) is from 35 to 85% by weight, preferably from 40 to 80% by weight, more preferably from 45 to 75% by weight based on the sum (100% by weight) of the (A), (B), (C) and (D) components.
When the compounding proportion of the polypropylene-based resin (A) is less than 35% by weight, the rigidity may decrease, while when over 85% by weight, the impact resistance may decrease.
The elastomer (B) used in the present invention is not particularly restricted, and preferably is one containing a rubber component. For example, an elastomer composed of vinyl aromatic compound-containing rubber and/or ethylene-xcex1-olefin random copolymer rubber, and the like are listed.
As the vinyl aromatic compound-containing rubber used in the present invention, block copolymers consisting of a vinyl aromatic compound polymer block and a conjugated diene-based polymer block, and the like are exemplified, and preferable are those in which suitably 80% or more, more suitably 85 or more of double bonds of the conjugated diene portion is hydrogenated. This rubber has Q value (a molecular weight distribution) according to a GPC method of preferably 2.5 or less, more preferably 2.3 or less. The average content of a vinyl aromatic compound in the vinyl aromatic compound-containing rubber is preferably from 10 to 20% by weight, more preferably from 12 to 19% by weight. Further, the melt flow rate (MFR, JIS-K-6758, 230xc2x0 C.) of the vinyl aromatic compound-containing rubber is preferably from 1 to 15 g/10 min., more preferably from 2 to 13 g/10 min.
Examples of the above-mentioned vinyl aromatic compound-containing rubber or the hydrogenated product thereof include block copolymers such as styrene-ethylene-butene-styrene-based rubber (SEBS), styrene-ethylene-propylene-styrene-based rubber (SEPS), styrene-butadiene-based rubber (SBR), styrene-butadiene-styrene-based rubber (SBS), styrene-isoprene-styrene-based rubber (SIS), and the like. A rubber obtained by reacting a vinyl aromatic compound such as styrene or the like with an olefin-based copolymer rubber such as an ethylene-propylene-non-conjugated diene-based rubber (EPDM) can also be used suitably. Further, two or more of vinyl aromatic compound-containing rubber may also be used together.
The production method of the above-mentioned vinyl aromatic compound-containing rubber is not particularly restricted, and there are listed, for example, a method in which a vinyl aromatic compound is bonded, by polymerization, reaction or the like, to an olefin-based copolymer rubber or conjugated diene rubber, and the like.
In the ethylene-xcex1-olefin random copolymer rubber used in the present invention, the xcex1-olefin is an xcex1-olefin having 3 or more carbon atoms, preferably 3 to 20 carbon atoms, more preferably 3 to 12 carbon atoms such as, for example, propylene, butene-1, pentene-1, hexene-1, heptene-1, octene-1, decene-1 and the like, and preferably propylene, butene-1, hexene-1 and octene-1.
Examples of the ethylene-xcex1-olefin random copolymer rubber include an ethylene-propylene random copolymer rubber, ethylene-butene-1 random copolymer rubber, ethylene-hexene-1 random copolymer rubber, ethylene-octene-1 random copolymer rubber and the like, and preferably an ethylene-octene-1 random copolymer rubber, ethylene-butene-1 random copolymer rubber and ethylene-propylene random copolymer rubber. Further, the ethylene-xcex1-olefin random copolymer rubbers may be used alone or in combination of two or more thereof.
The ethylene-octene-1 random copolymer rubber has a Q value (molecular weight distribution) according to a GPC method of preferably 2.5 or less, more preferably 2.3 or less. Further, the ethylene-octene-1 random copolymer rubber has an octene-1 content of preferably from 15 to 45% by weight, more preferably from 18 to 42% by weight. Furthermore, the ethylene-octene-1 random copolymer rubber has a melt flow rate (MFR, JIS-K-6758, 190xc2x0 C.) of preferably from 1 to 15 g/10 min., more preferably from 2 to 13 g/10 min.
The ethylene-butene-1 random copolymer rubber has a Q value according to a GPC method of preferably 2.7 or less, more preferably 2.5 or less. Further, the ethylene-butene-1 random copolymer rubber has a butene-1 content of preferably from 15 to 35% by weight, further preferably from 17 to 33% by weight. Furthermore, the ethylene-butene-1 random copolymer rubber has a melt flow rate (MFR, JIS-K-6758, 190xc2x0 C.) of preferably from 1 to 15 g/10 min., more preferably from 2 to 13 g/l min.
The ethylene-propylene random copolymer rubber has a molecular weight distribution (Q value) according to a GPC=method of preferably 2.7 or less, more preferably 2.5 or less. Further, the ethylene-propylene random copolymer rubber has a propylene content of preferably from 20 to 30% by weight, further preferably from 22 to 28% by weight. Furthermore, the ethylene-propylene random copolymer rubber has a melt flow rate (MFR, JIS-K-6758, 190xc2x0 C.) of preferably from 1 to 15 g/10 min., more preferably from 2 to 13 g/10 min.
The production method of the above-mentioned ethylene-xcex1-olefin random copolymer rubber is not particularly restricted, and the random copolymer rubber can be produced by copolymerizing ethylene with an xcex1-olefins by a known polymerization method, using a known catalyst. As the known catalyst, for example, a catalyst system consisting of a vanadium compound and an organic aluminum compound, a Ziegler-Natta catalyst system or a metallocene catalyst system, and the like are listed, and as the known polymerization method, a solution polymerization method, slurry polymerization method, high pressure ion polymerization method or gas phase polymerization method, and the like are exemplified.
The compounding proportion of the elastomer (B) is from 10 to 35% by weight, preferably from 15 to 30% by weight. When the content of the elastomer (B) is less than 10% by weight, impact strength of the thermoplastic composition may decrease, while when over 35% by weight, the rigidity and heat resistance may decrease.
The inorganic filler (C) is not particularly restricted so far as the rigidity is improved. For example, calcium carbonate, barium sulfate, mica, crystalline calcium silicate, talc, magnesium sulfate fiber and the like are listed. Preferable are talc and/or magnesium sulfate fiber.
Talc used in the present invention is not particularly restricted, and preferable is one obtained by grinding water-containing magnesium silicate. The crystalline structure of molecules shows a pyrophyllite type three-layered structure and the talc includes lamination of this structure, and particularly, a plate-like powder in which the crystal is finely pulverized to about unit layer is preferable.
Talc used in the present invention has an average particle size of preferably 3 xcexcm or less. The average particle size of talc means a 50% equivalent particle size D50 determined from an integrated distribution curve by a minus sieve method made by suspending the talc in a dispersing medium such as water and alcohol and measuring the particle sizes using a centrifugal sedimentation type particle size distribution measuring apparatus.
Talc may be used itself without treatment, or may be surface-treated with known various silane coupling agents, titanium coupling agents, higher fatty acids, higher fatty esters, higher fatty amides, higher fatty salts or other surfactants before use for the purpose of improving interfacial adhesion with the polypropylene-based resin (A) and dispersability.
The magnesium sulfate fiber is not particularly restricted, and has an average fiber length of preferably from 5 to 50 xcexcm, more preferably from 10 to 30 xcexcm. The magnesium sulfate fiber has an average fiber diameter of preferably from 0.3 to 2.0 xcexcm, more preferably from 0.5 to 1.0 xcexcm.
The compounding proportion of the inorganic filler (C) used in the present invention is from 2 to 30% by weight, preferably from 5 to 30% by weight, more preferably from 10 to 30% by weight. When the proportion of the inorganic filler is less than 2% by weight, the rigidity may decrease, while when over 30% by weight, impact strength may be insufficient, and further, appearance may also deteriorate.
The resin (D) used in the present invention is a resin which can improve the swelling ratio (SR) of a polypropylene-based resin composition, and has a melt tension (MT) measured at a temperature of 190xc2x0 C. and a winding rate of 15.7 m/min. of 0.1 N or more, preferably 0.15 N or more. When this melt tension (MT) is less than 0.1 N, appearance of a molded article may be insufficient.
The resin (D) has a swelling ratio (SR) measured at a temperature of 220xc2x0 C., an L/D ratio of an orifice of 40 and a shearing rate of 1.2xc3x97103 secxe2x88x921 of 1.8 or more, preferably 2.0 or more. When this swelling ratio (SR) is less than 2.0, appearance of a molded article may be insufficient.
The time required until the ratio (G(t)/G(0.02)) of the relaxation modulus G(t) of the resin (D) measured at 210xc2x0 C. to the relaxation modulus G(0.02) in a time of 0.02 sec. thereof measured at 210xc2x0 C. reaches 0.01 is 10 sec. or more, preferably 15 sec. or more. When the time required until the ratio (G(t)/G(0.02)) of the relaxation modulus G(t) measured at 210xc2x0 C. to the relaxation modulus G(0.02) in a time of 0.02 sec. reaches 0.01 is less than 10 sec., appearance of a molded article may be insufficient.
As the resin (D) used in the present invention, for example, a polypropylene block copolymer and/or a polypropylene master batch of polytetrafluoroethylene fiber and the like are listed.
The polypropylene block copolymer is preferably an ethylene-propylene block copolymer, further preferably an ethylene-propylene block copolymer composed of propylene homopolymer portion and an ethylene-propylene copolymer portion, having a intrinsic viscosity [xcex7]EP of the ethylene-propylene copolymer portion of from 8 to 15 dl/g and a content of the ethylene-propylene copolymer portion of from 20 to 40% by weight.
The amount of the resin (D) used in the present invention is 0.1% by weight or more and less than 5% by weight, preferably from 0.5 to 4.5% by weight, further preferably from 1.0 to 4.5% by weight based on the sum of the components (A), (B), (C) and (D). When the amount of the resin (D) is less than 0.1% by weight, appearance of a molded article may be insufficient, while when 5% by weight or more, the flowability of the thermoplastic plastic composition may decrease.
The thermoplastic resin composition of the present invention can be produced using a kneader such as a single-screw extruder, twin-screw extruder, Banbury mixer, heat roll or the like. Addition and mixing of components into a kneader can be conducted simultaneously or divisionally, and for example, the following methods are listed, but it is not limited thereto.
(Method 1)
A method in which a polypropylene-based resin (A) and an inorganic filler (C) are kneaded, an elastomer (B) is added to the mixture, and then, a resin (D) is kneaded with the resulting mixture.
(Method 2)
A method in which an inorganic filler (C) is previously kneaded in high concentration with a polypropylene-based resin (A) to obtain a master batch, the master batch is diluted with a polypropylene-based resin (A), an elastomer (B) or the like, and then, a resin (D) is kneaded with the resulting mixture.
(Method 3)
A method in which a polypropylene-based resin (A) and elastomer (B) are kneaded, an inorganic filler (C) is added to the mixture, and then, a resin (D) is kneaded with the resulting mixture.
(Method 4)
A method in which an elastomer (B) is previously kneaded in high concentration with a polypropylene-based resin (A) to obtain a master batch, a polypropylene-based resin (A) and an inorganic filler (C) are added to the master batch, and then, a resin (D) is kneaded with the mixture.
(Method 5)
A method in which a polypropylene-based resin (A) and an inorganic filler (C), and a polypropylenee-based resin (A) and elastomer (B) are previously kneaded, respectively, thereafter, they are combined, and then, a resin (D) is kneaded with the resulting mixture.
The kneading temperature is usually from 170 to 250xc2x0 C., more preferably from 190 to 230xc2x0 C. The kneading time is usually from 1 to 20 minutes, more preferably from 3 to 15 minutes.
Further, in these kneaders, additives such as an antioxidant, ultraviolet absorber, lubricant, pigment, antistatic agent, copper inhibitor, flame retardant, neutralizing agent, foaming agent, plasticizer, nucleating agent, foam inhibitor, cross-linking agent and the like may also be appropriately compounded in the range wherein the object and effect of the present invention are not lost, in addition to the components (A), (B), (C) and (D) used in the present invention.
The thermoplastic resin composition of the present invention can be generally molded into an injection-molded article by a known injection molding. Particularly, the injection-molded article is suitably used as parts for automobiles such as a door trim, pillar, instrumental panel, bumper and the like.